Remote monitoring of patients engaged in rehabilitation programs offers the potential of maximizing clinical outcomes and minimizing costs. With initial funding from a Coulter Translational Research Partnership in Biomedical Engineering and from the Washington Research Foundation, JointMetrix Medical LLC has developed a prototype system that monitors joint motion and recognizes patient activity for an entire day in the patient's own environment. Through the use of Smartphone technology, the data will be automatically uploaded via a patient-friendly App to an established IDTF (Independent Diagnostic Testing Facility - eCardio) where a report to the rehabilitation team can be generated. The company has also recruited a seasoned management team with extensive high-level experience in remote monitoring and has already attracted interest from two major companies engaged in providing implants to treat patients with osteoarthritis. In this Phase I proposal we seek funds for the development, validation, and testing of a missing element of the system: a low-cost, reliable, and valid joint motion sensor. Realizing that any of the relatively expensive existing options for sensing would be cost prohibitive, we incorporated a low-cost flex sensor into the current prototype system. However, this sensor has been shown in our preliminary studies to have crucial limitations that make it unsuitable for a production system. We propose to adopt fiber optic sensing technology and to integrate this into the existing package of electronics. The system will gather data in a store-and-forward mode until the end of the monitoring day when the phone App will direct the patient to answer a series of questions about their progress. Once the responses are complete, the sensor data and the patient responses will be uploaded to a server at the IDTF where a report will be automatically generated and forwarded to the rehabilitation team. In these initial studies, we will concentrate on recognizing patients who are not progressing well in rehabilitation post-joint replacement so that they can be brought back for examination and further treatment in order to prevent costly complications. We intend to monitor patient function on selected days during the first 3 months after surgery - a time period when 5-10% of patients are currently re-admitted to the hospital for joint manipulation. We have assembled a team of biomechanical, rehabilitation, orthopaedic, and information technology experts supported by an experienced medical device management team to carry out the proposed project. Following the new hardware development, we will test the feasibility of the new system by up to 12-hour data collection sessions in free-living individuals using an already approved IRB protocol. At the end of the Phase I studies, we will be in a strong position to begin characterizing activity profiles in a group of patients in order to tain the activity recognition and to prepare for a full-scale clinical trial of effectiveness in a PhaseII application.